Fuel tanks in automotive vehicles, passenger vehicles in particular, take on a variety of shapes. Fuel tanks for passenger vehicles (which includes trucks such as pick-up trucks) tend to conform to “left over space” by vehicle designers so there is no common design shapes between vehicle models. These fuel tanks are often made of inexpensive polymers or metals using simple forming techniques, such as blow molding or stamping. Fuel vessels for gaseous fuels for future vehicles, particularly those for passenger vehicles, will likely not receive much relief from the foregoing constraints.
The use of gaseous fuels, such as hydrogen or compressed natural gas, for vehicles is generally known. Such fuels can represent an alternative to petroleum as a fuel source for automotive vehicles, but are generally required to be stored at an elevated or high pressure in a storage vessel. Typical storage vessels and their associated mounting systems for compressed gaseous fuels include various components that can raise the cost and complexity of manufacturing an alternative fuel vehicle. In addition, such storage vessel systems often result in a loss of interior cabin volume or trunk volume in an automotive vehicle. Also, such storage vessel systems often utilize one or more cylindrical storage vessels which can present difficulties in fitting the storage vessel system into available space in the vehicle and may require modifying aspects of the vehicle that surround the storage vessel system. The lower storage density of the gaseous fuels compared to gasoline or diesel fuel further exasperates the problem.
Current technologies for high pressure storage vessels typically employ either metal or filament wound cylinders. The drawbacks of these designs include cost and the inability to package efficiently in vehicle architectures.
It is known that at a given pressure, the smaller the diameter of a spherical or cylindrical pressure vessel, the smaller the wall thickness required to contain the pressure. This is represented by the following equation:
      T    m    =                    PD        o                    2        ⁢                                  ⁢                  S          o                      →                  T        m            ∝              D        o            Where Tm=min. pipe thickness, P=internal pressure, Do=diameter of the pipe, and So=tensile strength of the material of which the pipe is made. Based on this relationship, a larger pressure vessel may be constructed from a combination of many smaller tubes and/or spheres. The simplest example would be an array of small diameter tubes arranged in a cubic closed packing (ccp) or hexagonal tube packing structure. Examples of previous attempts to construct conformable pressure vessels based on the small diameter concept include polymeric/aluminum foam, glass microspheres, dog bone concepts, and pillow concepts. The polymeric/aluminum foam concept involves the use of polymeric or metallic foam to create thousands of small spheres packed into a fuel vessel shape.
The glass microspheres concept by the Savannah River National Lab and Alfred University applied the concept of small diameter thin wall pressure vessels in the form of hollow glass microspheres. These spheres could be poured into any shape of vessel desired. However, the glass microspheres required high energy microwaves to open pores that would allow gas in/out.
The dog bone concepts by Lawrence Livermore National Lab utilized the concept of internal load bearing structures to alleviate pressure from the skin. This concept however was still limited to simple geometric shapes such as cubes and introduced many potential leak points at all the joints.
The pillow concepts typically blended several conventional vessels together to provide a flatter shape. They worked on the basis that sections of the vessel that butted against each other would lead to forces that cancel each other out and thus allow a more conformable shape. While a number of these concepts were successful in retaining the desired pressure, they were bulky, heavy and expensive to manufacture.
Thus, there remains a need in the relevant art for a conformable high pressure gaseous fuel storage system that overcomes the aforementioned and other disadvantages.